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2 Cell signaling mediates: reaction to signals from environment communication between cells teamwork of cells in multicell organism Signaling pathway includes: Signal cells - produce specific type of signal molecules Signal molecules hydrophilic - large, do not diffuse through the membrane (proteins) hydrophobic - small, less numbered, difuse through the membrane (steroids, NO, gases) Receptores - located on target cell, can distinguish signal molecule and specifically react to it (one type of receptor to one type of signal) Target cells - transfer the extracellular signal to intracellular and thus control the cell behavior

3 Stages of cell signaling 1. Reception chemical message (signal molecule) binds to a protein (receptor) on the cell surface 2. Transduction binding of the signal molecule alters the receptor protein signal usually starts a cascade of reactions known as signal transduction pathway there is usually amplification and modulation of signal 3. Response transduction pathway finally leads to response responses can vary from turning on a gene, activating an enzyme, rearranging the cytoskeleton

6 4. CYTOKINS - proteins produced by cell as a signals for proliferation, differentiation or survival of cells interleukins produced by lymfocytes interferons induction of resistence against viruses tumor necrotizing factors inhibition of cell division grow factors stimulation of proliferation and differentiation

12 TYPES OF RECEPTORS 1. receptors connected with ion channels signal = flow of ions across the membrane change of membrane potential (electric event) nerve impuls in membrane of nerve and muscle cells 2. receptors connected with G-proteins (the largest family of receptors) G-protein one polypeptid chain three subunits,, 7x goes through the membrane is activated by GTP from GDP

23 Tyrosine-Kinase receptors part of the receptor on the cytoplasmic side serves as an enzyme which catalyzes the transfer of phosphate groups from ATP to the amino acid Tyrosine on a substrate protein

25 PROTEIN KINASES = KINASES ACTIVATION OF PROTEINS = PHOSPHORYLATION (ATP is used as a donor of phosphate group) In human, there is about 2 % of genes for protein kinases, in cell can be about 1000 protein kinase at the same moment

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